The fundamental steps of processing color light-sensitive materials generally include a color developing step and a desilvering step. Thus, an exposed color light-sensitive material is introduced into a color developing step, where silver halide is reduced with a color developing agent to produce silver and the oxidation product of color developing agent in turn reacts with coupler to yield a dye image. Subsequently, the color light-sensitive material is introduced into a desilvering step, where silver produced in the preceding step is oxidized with an oxidizing agent (usually called a bleaching agent), and dissolved away with a silver ion complexing agent usually called a fixing agent. Therefore, only a dye image is formed in the thus processed color light-sensitive material. In addition to the above described two fundamental steps of color development and desilveration, actual development processing involves auxiliary steps for maintaining the photographic and physical quality of the resulting image or for improving the preservability of the image. For example, there are illustrated a hardening bath for preventing a light-sensitive layer from being excessively softened during color photographic processing, a stopping bath for effectively stopping the developing reaction, an image stabilizing bath for stabilizing the image, and a layer removing bath for removing the backing layer on the support.
The above described desilvering step may be conducted in two ways: one way used two steps employing a bleaching bath and a fixing bath; and the other way is more simple and is conducted in one step employing a bleach-fixing bath containing both a bleaching agent and a fixing agent for the purpose of accelerating the processing and labor elimination.
Ferricyanide and ferric chloride, heretofore used as bleaching agents, are good bleaching agents due to their high oxidizing power. However, a bleaching solution or bleach-fixing solution containing ferricyanide as a bleaching agent can release poisonous cyanide by photolysis causing environmental pollution. Accordingly, waste processing solutions thereof must be rendered harmless in view of environmental pollution. A bleaching solution containing ferric chloride as a bleaching agent is not desirable because materials of vessels in which the solution is retained are liable to be corroded due to the extremely low pH and high oxidizing power of the solution. In addition, iron hydroxide is precipitated in an emulsion layer during a water-washing step after a bleaching step using ferric chloride, resulting in staining.
On the other hand, potassium dichromate, quinones, copper salts, etc., which have been used as bleaching agents have weak oxidizing power and are difficult to handle.
In recent years, bleach processing using a ferric ion complex salt (e.g., aminopolycarboxylic acid-ferric ion complex salt, particularly iron (III) ethylenediaminetetraacetate complex salt) as a major bleaching bath component has mainly been employed in processing color light-sensitive materials in view of the acceleration and simplification of the bleaching provided and the need to prevent environmental pollution.
However, ferric ion complex salts have a comparatively low oxidizing power and, therefore, have insufficient bleaching power. A bleaching or bleach-fixing solution containing such a complex salt as a bleaching agent can attain some desirable objects when bleaching or bleach-fixing a low speed color light-sensitive material containing, for example, a silver chlorobromide emulsion as a major component. However, such a solution fails to fully desilver due to insufficient bleaching power or requires a long time to bleach when processing a high speed, spectrally sensitized color light-sensitive material containing a silver chlorobromoiodide emulsion or a silver iodobromide emulsion as a major component, particularly color reversal light-sensitive materials for photographing or color negative light-sensitive materials for photographing comprising an emulsion containing a larger amount of silver.
Other known bleaching agents than ferric ion complex salts include persulfates. Persulfates are usually used in a bleaching solution together with a chloride. However, this persulfate-containing bleaching solution has less bleaching ability than ferric ion complex salts, thus requiring a substantially long period of time for bleaching.
As described above, bleaching agents which do not cause environmental pollution or corrode vessels and apparatus have only a weak bleaching ability. Hence, it is requested to enhance the bleaching ability of a bleaching solution or a bleach-fixing solution containing a weak bleaching agent, particularly a ferric ion complex salt.
In order to raise the bleaching ability of a bleaching solution or a bleach-fixing solution containing a ferric ion complex salt such as iron (III) ethylenediaminetetraacetate as a bleaching agent, it has been proposed to add various bleach accelerating agents to the processing bath.
Examples of such bleach accelerating agents include 5-membered heterocyclic mercapto compounds as described in British Pat. No. 1,138,842, thiadiazole derivatives as described in Swiss Pat. No. 336,257, thiourea derivatives, and thiazole derivatives, etc. However, these compounds do not necessarily have sufficient bleach accelerating effects when they are added to a bleaching solution or a prebath thereof. Also, only insufficient bleach accelerating effects are obtained when they are added to a bleach-fixing solution or a prebath thereof. Further, in the latter case they react with silver ions present in the bleach-fixing solution to form precipitate which creates many troubles. For example, the precipitate chokes up filters of a circulation system in an automatic processing machine and it adheres on color light-sensitive materials, resulting in stain formation.
A processing method is also known wherein a 5-membered heterocyclic compound containing two or three nitrogen atoms as ring constituting members and having at least one mercapto group is added to a bath just before a bath of the bleaching processing as described in Japanese Patent Application (OPI) No. 52534/79. However, when these compounds are directly added to a bleaching solution or a bleach-fixing solution, sufficient bleach accelerating effects cannot be obtained. In addition, they lack stability in the processing solution and cannot endure use for a long period of time.
Moreover, thiourea derivatives as described in Japanese Patent Publication No. 8506/70 (corresponding to British Pat. No. 1,150,466) and U.S. Pat. No. 3,706,561, and selenourea derivatives as described in Japanese Patent Application (OPI) No. 280/71 (corresponding to U.S. Pat. No. 3,701,662) are known as bleach accelerating agents. However, many of these bleach accelerating agents do not always show a satisfactory bleach accelerating effect, or some of them lack stability in the processing solution although they have a good bleach accelerating effect. Therefore, they provide a processing solution having only a short effective life or which cannot be stored for a long time.
Furthermore, heterocyclic alkylmercaptan derivatives as described in Japanese Patent Application (OPI) No. 32736/ 78, and aminoalkylmercaptan derivatives as described in U.S. Pat. No. 3,893,858 are known as bleach accelerating agents. However, these bleach accelerating agents do not always show a satisfactory bleach accelerating effect, or they retard fixing even although they can accelerate bleaching. Therefore, a long period of time is necessary for desilvering processing.
In addition, mercaptothiadiazole derivatives having at least one group selected from a carboxy group and a sulfo group as described in Japanese Patent Application (OPI) No. 28426/78 are known as bleach accelerating agents. However, these compounds do not always show a satisfactory bleach accelerating effect in order to carry out desilvering processing for a shorter period of time.